1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copier, a facsimile machine, and a printer, and to a lubricant applicator, a process cartridge, and a transfer unit adopted in the image forming apparatus.
2. Description of the Related Art
To improve cleaning and transfer performance of a photoconductor or an intermediate transfer belt functioning as an image carrying member and prolong the life thereof, typically a lubricant applicator is used that applies lubricant to a surface of the image carrying member. In a typical configuration of the lubricant applicator, an application roller functioning as a lubricant applying member, such as a brush roller and a sponge roller, is rotatably provided such that the outer circumferential surface thereof is in uniform contact with the surface of the image carrying member. A solid lubricant, such as solidified zinc stearate, is biased against the application roller, and is brought into contact with the application roller with a predetermined pressure. A biasing member for biasing the solid lubricant toward the application roller uses, for example, the weight of the solid lubricant itself, a weight biasing the solid lubricant, or the resilience of a compressed spring. With this configuration, the application roller scrapes and applies the solid lubricant to the surface of the image carrying member as the image carrying member rotates.
In a new lubricant applicator having the above-described configuration, the force of the brush roller pushing back against the solid lubricant is relatively high due to, for example, the smooth surface of the solid lubricant at the beginning and relatively high resilience of bristles forming the brush roller. With the pressure applied by the biasing member alone, therefore, the solid lubricant fails to come into uniform contact with the brush roller, thereby limiting penetration of the solid lubricant into the brush roller. As a result, the area of contact between the solid lubricant and the brush roller is also reduced, reducing the amount of abrasion of the solid lubricant by the brush roller. In the initial stage of use of the lubricant applicator, therefore, the amount of the lubricant applied to the surface of the image carrying member is insufficient.
To prevent such a shortage of the lubricant application amount in the initial stage of use, it is conceivable to increase the pressure of the solid lubricant applied to the brush roller by the biasing member. If, the pressure applied by the biasing member is increased, however, the lubricant application amount is excessively increased as the area of contact is increased due to an increase over time in the amount of penetration of the solid lubricant into the brush roller. Consequently, accelerated consumption of the solid lubricant and cleaning failure occur in some cases.
In view of the above, the present applicant has proposed a lubricant applicator, in which the solid lubricant is reciprocally movable toward and away from the brush roller, and which includes regulating members for regulating the solid lubricant not to separate from the brush roller by more than a predetermined distance due to the force of the brush roller pushing back against the solid lubricant when the solid lubricant is biased toward the brush roller by the biasing member (JP-2007-058169-A). In the device, the regulating members prevent the solid lubricant from separating from the brush roller by more than the predetermined distance, forcing the solid lubricant constantly into the brush roller by at least a predetermined amount. Even in the initial stage of use of the device, therefore, the amount of abrasion of the solid lubricant is increased with at least a predetermined area of contact maintained between the solid lubricant and the brush roller, and the shortage of the amount of the solid lubricant applied to the image carrying member is prevented.
Further, as time elapses, the force of the brush roller pushing back against the solid lubricant is reduced. Thus, the solid lubricant is brought into uniform contact with the brush roller, increased in the area of contact thereof with the brush roller, and prevented from separating from the brush roller by more than the predetermined distance. In this state, regulation by the regulating members ends. Thus, the device switches to a state in which the solid lubricant is brought into contact with and scraped by the brush roller solely with the biasing performed by the biasing member. The biasing member is adjusted to bias the solid lubricant toward the brush roller with pressure for scraping an appropriate amount of the solid lubricant in a stable contact state with an increased contact area. Accordingly, the appropriate amount of the solid lubricant is stably applied over time.
Meanwhile, a new spare lubricant applicator may be installed in place for at least a few months to a year until actual use thereof. In the initial state of the lubricant applicator described above, the solid lubricant penetrates into the brush roller due to the forcible application of pressure by the regulating members. In the new spare lubricant applicator, therefore, the solid lubricant penetrating into the brush roller may be left standing for a long time. If the solid lubricant in such a state is left standing for a long time, bristles of the brush roller are flattened at a position at which the solid lubricant penetrates into the brush roller. When the new lubricant applicator starts being used in place of the old device, therefore, an abnormal image may be generated in the form of banding, for example, that is caused by uneven rotation of the brush roller.
The occurrence of the above-described phenomenon is not limited to prolonged exposure without use of the new lubricant applicator. The phenomenon may also occur when the new lubricant applicator is used for only a short time after installation thereof and thereafter left standing for along time without being actuated, or when the lubricant applicator is detached and left standing. This is because the flattening of the bristles of the brush roller similarly occurs when the lubricant applicator is left standing for a long time in the initial stage of use, in which the regulating members forcibly apply the pressure of the solid lubricant to the brush roller.
The above phenomenon has been described in terms of the flattening of the bristles of the brush roller as the deformation of the lubricant applying member. However, the deformation is not limited thereto. A similar phenomenon occurs when a sponge roller is used as the lubricant applying member. That is, the sponge roller deforms in the area of contact thereof with the solid lubricant forcibly applied with pressure by the regulating members, when the lubricant applicator is left standing for a long time before use or in the initial stage of use thereof.